Liquid dispensers for dispensing soaps and the like are well known. A large number of dispensers for dispensing for example hand cleaning soaps dispense the liquid itself. In many applications it is preferable to dispense the soap in the form of a foam. Foams tend to be much easier to spread than the corresponding liquid and in addition there is much less waste due to splashing or run-off since the foam has a much higher surface tension than the liquid. A foam requires much less liquid to produce the same cleaning power as obtained with the un-foamed liquid due to the much higher surface area of the former.
Known prior art foaming devices are generally of two types. In the first type of foamer, such as disclosed in U.S. Pat. Nos. 4,019,657 and 3,709,437 the foam is produced by a jet of air. A disadvantage of this first type of foamer is that the quality of the foam varies as the dispensing force is varied.
The second type of foam dispenser, as disclosed in U.S. Pat. Nos. 3,422,993 and 3,985,271 uses a porous material through which the foamable liquid is pumped thereby mixing the liquid with air to form the foam. Drawbacks to this type of foamer is that a considerable amount of pressure is required to force the liquid through the porous material. A further drawback to both types of foam dispensers is that the foamer is located at the top of the dispenser and a tube extends down to the bottom of the liquid storage container so that considerable force must be applied to pump the liquid up into the foamer and to dispense it therefrom.
Examples of other dispensers constructed on this principle are disclosed in EP-A-392 238, EP-A-565 713 and EP-A618 147 are all directed to liquid dispensers comprising a bottle with a hand operated pump in the neck of the bottle. Each of the devices disclosed in these references include a hose which extends to the bottom of the bottle so that the liquid must be pumped up against gravity into the mixing chamber. As stated above, a major disadvantage to these configurations is that as the liquid is depleted greater force must be exerted in the pumping procedure in order to raise the liquid from the bottom of the container during dispensing of the liquid. These types of dispensers are also limited in the sense that they must be used in the upright vertical position.
In many of the prior art foaming devices the foamer unit is separate from the container holding the liquid. When the liquid container is replaced the operator generally has to interconnect the foamer unit with the liquid container which can be an inconvenience. It would therefore be advantageous to provide a foam dispenser which allows convenient and rapid replacement of the liquid container in the dispenser.
Liquid detergents or soaps for hand cleaning generally require preservatives to increase shelf life of the detergent. Antioxidants are typically present as an additive to reduce oxidation of the soap in the presence of air normally present in the soap container and this adds to the cost of the soap. In the presence of air many soaps tend to thicken which requires increasing force to dispense the liquid. The thickened liquid is prone to clogging up the dispensing pathway. The dispenser bottles disclosed in EP-A-392 238, EP-A-565 713 and EP-A-618 147 are all vented to prevent negative pressure in the bottles from building up as liquid is pumped out of the bottles. Commonly owned U.S. Pat. No. 5,445,288 discloses a foaming device using a collapsible container.
Accordingly, it would be advantageous to provide a dispenser which produces and dispenses a liquid in the form of foam and in which the liquid is not exposed to air until expelled from the liquid container portion of the dispenser.